1. Field of the Invention
This invention relates to distillation column internals, particularly distillation trays and an assembly of such trays, to distillation columns including such trays, and to systems utilizing such distillation columns. This invention is directed to a specific construction of distillation trays and an assembly of these trays that, when mounted in a distillation column, provide indirect heat exchange of a fluid with liquid and vapor in the chamber of the distillation column.
2. Description of the Prior Art
The principles and design procedures of distillation to separate a material containing two or more components by boiling the material in liquid form are described in my book entitled "Distillation" published in 1961 by Reinhold Publishing Corporation, New York, N. Y. One of the chapters of the book is directed particularly to column internals including distillation trays. Of the various types of trays of the prior art described in that chapter the most pertinent type of tray is Turbogrid trays that have long narrow slots that could be considered as modified sieve trays. Sieve trays are merely plates perforated with small holes. The Turbogrid trays are made either by stamping slots out of a flat metal plate or by the use of parallel metal bars or slats spaced from one another to provide many long narrow slots for each tray.
As described also in my book mentioned above, there are two types of distillation trays broadly speaking. These are referred to as cross-flow trays and shower-type trays. The former type has a downcomer that carries the liquid to the next lower tray. That liquid flows across the tray and then over a weir to the downcomer. Turbogrid trays are recommended for use as shower-type trays, although they could be used with downcomers. An assembly of vertically tiered distillation trays are disposed within the rectifying section of a distillation column and another assembly of such trays are disposed in the stripping section of the column. The liquid feed is introduced into the column between these two sections.
As mentioned above, the special utility of the invention is in the field of cryogenic distillation, particularly low-temperature distillation of a product from the steam-cracking of light hydrocarbons, to separate ethylene from other components in the cracked gaseous product. A description of low-temperature processing of such cracked gases is presented in the 1946 article entitled "Low Temperature Processing of Light Hydrocarbons" by A. W. Pratt and N. L. Foskett in Transactions of American Institute of Chemical Engineers, vol. 42, pages 149-163. With respect to the systems of the present invention, other relevant publications include: the article entitled "Cracked-gas quenching, compression" by S. B. Zdonik et al. in The Oil and Gas Journal, Nov. 24, 1969, at pages 96-101; the article entitled "Low-pressure demethanization techniques for ethylene plants" by W. K. Lam et al. in The Oil and Gas Journal, May 18, 1970, beginning at page 111; the article entitled "Cryogenic gas-processing plant goes on stream in West Virginia" appearing in the Nov. 24, 1969, issue of The Oil and Gas Journal at pages 81-83; and the article entitled "New Flow Sequence for Ethylene Plants" in Hydrocarbon Processing, June, 1970, at page 13. With respect to one of the systems of the present invention, one system of the prior art that is generally relevant is U.S. Pat. No. 3,444,696. In none of the prior art including the articles and patent mentioned above is there any disclosure of a distillation tray that is constructed to function also for a heat exchange between liquid and vapor in the column with liquid passing through an assembly of such trays.